Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $166.25   10.773%   $184.1601   $184.16   $184.15   $184.20  
  Purchase #2 $183.65   8.651%   $199.5376   $199.54   $199.55   $199.50  
  Purchase #3 $35.69   11.367%   $39.7469   $39.75   $39.75   $39.70  
  Purchase #4 $167.93   3.775%   $174.2694   $174.27   $174.25   $174.30  
  Purchase #5 $120.42   5.867%   $127.485   $127.49   $127.50   $127.50  
  Purchase #6 $250.30   11.361%   $278.7366   $278.74   $278.75   $278.70  
  Purchase #7 $63.58   4.424%   $66.3928   $66.39   $66.40   $66.40  
  7 purchase totals = $987.82       $1,070.3284   $1,070.34   $1,070.35   $1,070.30